DE2755505C2 - Means for the sustained release of a biological agent - Google Patents

Description

The invention relates to a means for delivering a biologically active substance into a human or animal body according to the preamble of the preceding patent claim 1.

Various delivery means are already known which consist of a polymeric carrier material in combination with a biologically active substance. For example, British Patent 1,135,966 discloses pharmaceutical preparations which consist of a polymeric hydrogel (prepared by copolymerization of a hydrophilic monoolefinic monomer with 0.1 to 5% of a cross-linking agent) into which a soluble biologically active substance is incorporated. US Patent 3,857,932 describes drug-containing implantation dosage forms with a delayed release of the active ingredient which contain a water-insoluble hydrophilic polymer which is selected from polymers of hydroxy-lower alkyl (meth)acrylates or hydroxy-lower alkoxy-lower alkyl (meth)acrylates. US Patent 3,975,350 discloses, among other things, delayed release carrier systems which contain a biologically active agent and a hydrophilic cross-linked polyurethane. Finally, DT-PS 25 28 068 describes, inter alia, drug carrier systems which contain a drug and a water-insoluble hydrophilic copolymer which contains (A) 30-90% of a hydrophilic polymer derived from one or more monoolefinic monomers and (B) 10-70% of a hydrophobic polymer with terminal diolefinic groups.

The copolymer described in more detail in the characterising part of the present patent claim 1 has the following advantageous properties compared to the known carriers:

(1) Because of its linear structure, the copolymer is soluble in common organic solvents. This is important for biological applications because the copolymer can be purified and because solution casting techniques can be used for fabrication purposes. In addition, the copolymer is thermoplastic and can be easily molded and extruded.

(2) It is largely insoluble and non-erodible in body fluids.

(3) It is compatible with sensitive body tissues and does not cause toxicity and related difficulties.

(4) The degree of hydrophilicity and therefore water swellability of the copolymer can be predetermined based on its composition. In use, the delivery agent of the invention is permeated by the body fluids, thus creating a diffusion path for the delivery agent to the adjacent body tissue. As a result, a delayed release of the biologically active agent results.

(5) When swollen in body fluids, it is a soft elastomer and can therefore adapt to body cavities. In addition, it does not irritate.

(6) As regards water solubility, a wide range of biologically active substances can be incorporated into the copolymer in solution or in suspension.

The biologically active substances used according to the invention are, for example, medicaments for the curative or therapeutic treatment of humans and animals, as well as substances which have desirable pharmacological properties but which do not actually have curative or therapeutic properties. An example of the latter type of substance is a contraceptive substance. Examples of biologically active substances suitable for incorporation into compositions according to the invention are: abortifaciens, hypnotics, sedatives, tranquilizers, anticonvulsants, muscle relaxants, anti-Parkinsonian agents, analgesics, antipyretics, anti-inflammatory agents, local anesthetics, antispasmodics, antiulcer agents, antimicrobials, antimalarials, hormonal agents, androgenic steroids, estrogenic and progestational steroids, sympathomimetics, cardiovascular agents, diuretics, antiparasitic agents, antitumor agents, hypoglycemic agents, contraceptive agents and nutritional agents. The biologically active substances used in the composition according to the invention can be slightly water-soluble, moderately water-soluble or highly water-soluble.

The device according to the invention is suitable either for incorporation into a body cavity, such as the vagina, or for implantation into body tissue. It can be shaped for the intended purpose by standard techniques.

The copolymers used in accordance with the invention fall into the class known as amphipathic materials. Such copolymers are linear block copolymers of the type ABABAB . . . , in which A represents the hydrophilic regions and B represents the hydrophobic regions. A suitable polyoxyalkylene is, for example, polyoxyethylene having a molecular weight of from 400 to 20,000. The hydrophobic regions B consist of a polyurethane which is generally obtainable from a diisocyanate such as an aromatic or aliphatic diisocyanate, for example 4,4'-diphenylmethane diisocyanate, toluene diisocyanate (2,4- and/or 2,6-isomers), 1,6-hexamethylene diisocyanate, isophorone diisocyanate or 4,4'-dicyclohexylmethane diisocyanate, and one or more dihydroxy compounds. Examples of the latter are alkylene glycols having not more than 6 carbon atoms, such as 2,4'-diphenylmethane diisocyanate, 1,6'-dicyclohexylmethane diisocyanate, and one or more dihydroxy compounds. B. ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol or 1,4-butylene glycol, and/or short-chain oxyalkylated diphenols, such as B. 1,1'-isopropylidene-bis-p-phenyleneoxydipropan-2-ol.

Preferred interpolymers contain 30 to 70 weight percent hydrophilic regions A and 70 to 30 weight percent hydrophobic regions B. A preferred polyoxyalkylene is polyoxyethylene having a molecular weight of 600 to 6000. A preferred diisocyanate is 4,4'-diphenylmethane diisocyanate because it reacts at a convenient rate without the need for a polymerization catalyst, which can be leachable and toxic. A preferred dihydroxy compound for use in block B is 1,1'-isopropylidene-bis-p-phenyleneoxy-2-dipropanol.

The buffer optionally present in the agent of the invention may be any biologically acceptable buffer such as sodium bicarbonate or a phosphate buffer. The purpose of the buffer is to maximize the reproducibility of the effect of an agent of the invention in humans or certain animals, when such reproducibility is desired, by standardizing the pH of the body fluid within the range of the agent when it is in the body.

The composition of the invention may be prepared, for example, by first preparing the polymeric component by any standard method and then incorporating the biologically active substance and optionally the biologically acceptable buffer into the copolymer by any standard method, for example by solution casting or by a compounding process. It will be appreciated that testing a particular copolymer to determine whether it is suitable for use in accordance with the invention is a relatively simple matter. The amount of any particular biologically active substance to be incorporated into a composition of the invention will be known to a person skilled in the art from personal knowledge and/or from the relevant literature. However, it can also be readily determined by such a person by simple experiment. Likewise, the composition and amount of any buffer which may be present in a composition of the invention will be obvious or readily ascertainable by a person skilled in the art.

A particularly useful embodiment of the invention consists of an intravaginal composition containing an abortifaciens.

A suitable abortifacient is, for example, an abortifying prostaglandin derivative such as fluprostenol sodium [racemic sodium salt of (9S,11R,15R)-9,11,15-trihydroxy-16-(3-trifluoromethylphenoxy)-17,18,19,20-tetranor-5-cis,13-transprostadienoic acid]. A particularly preferred embodiment of the invention consists of an intravaginal agent which comprises fluprostenol sodium, a biologically acceptable buffer such as B. a phosphate buffer, and a hydrophobic copolymer, the latter having been obtained according to the above procedure and containing 60 wt.% polyoxyethylene with a molecular weight of 4000 and 40 wt.% hydrophobic polyurethane blocks which have been obtained from approximately equal parts by weight of 4,4'-diphenylmethane diisocyanate and 1,1'-isopropylidene-bis-p-phenyleneoxy-dipropan-2-ol.

The rate of in vivo release of the abortifacient from said intravaginal agent of the invention is determined by the composition of the copolymer, the size, shape and thickness of the agent, the nature and amount of the abortifacient and the nature and amount of the buffer in the agent. Said intravaginal agent may be in the form of discs, rings, blocks or plates or any other shape which is retained in the vagina.

The invention is further illustrated by the following examples:

example 1 (a) Preparation of a copolymer/drug mixture

Solutions of fluprostenol sodium (5 mg) in water (0.5 ml) and of C14-labeled fluprostenol sodium (5 µl at a concentration of 1 mg/ml, specific activity 133 µCi/mg) in water were added to a solution of the elastomer described below (10 g) in tetrahydrofuran (40 g). The solution was cast as a film in the usual manner. The resulting film was dried at room temperature for 24 hours in air and finally in vacuum for 8 hours at 70°C. The resulting polymer/drug mixture was molded under pressure at 110°C to give a platelet 0.1 cm thick.

The desorption of the drug and the radioactivity of 2 g of the mentioned plate in water at 37°C using a stirring speed of 100 rpm was shown to behave approximately according to the equation: &udf53;np30&udf54;&udf53;vu10&udf54;&udf53;vz2&udf54;&udf53;vu10&udf54;where
M _t is the amount of drug delivered in time t ,
M _∞ stands for the total amount of drug in the platelet,
t stands for time,
l is the thickness of the plate, and
D stands for the diffusion coefficient.

The plot of M _t / M _∞ versus t 1/2/l is a straight line which gives a value for D of approximately 5 × 10 ^-4 cm² st ^-1 .

Under sinking conditions (i.e., when the concentration of the drug in the medium into which it is released is very low) in vitro, this disk (0.1 cm thick) releases about 85% of the total drug in 4 h, whereas a corresponding disk of 0.17 cm thickness achieves this release in about 8 h.

(b) Preparation of the copolymer

The copolymer used in the preparation of the above-mentioned copolymer/drug mixture was obtained as follows:

A mixture of polyethylene glycol (600 g; molecular weight ca. 4000) and powdered magnesium silicate (18 g) was heated in vacuum to 110°C for 2 hours. The hot mixture was filtered to give a polyol which was dry and free from alkaline residues.

4,4'-Diphenylmethane diisocyanate (91.6 g) was melted and heated to 80°C. To this was added a mixture of diethylene glycol (3.3 g), 1,2-propylene glycol (2.3 g) and 1,3-butylene glycol (2.8 g). The resulting mixture was stirred at 80°C for 2 h. In this way, a clear viscous diisocyanate derivative with an isocyanate value of 23 wt.% was obtained, which was used according to the procedure below.

The above polyol (80 g) and dry 1,1'-isopropylidene-bis-p-phenyleneoxy-2-propanol (34 g) were mixed at 80°C to give a clear solution. To this was added the above diisocyanate derivative (46 g). The mixture was kept at 70-80°C for 18 hrs. The mixture was then cooled to room temperature and post-cured for 1 week at room temperature to give a soft, flexible elastomer. This was purified by dissolving in a mixture of acetone (1500 ml) and water (500 ml). To this solution was added a solution of sodium carbonate (5 g) in water (50 ml). The resulting mixture was stirred for 2 hrs at room temperature. The elastomer was precipitated by adding the polymer solution to vigorously stirred water (ca. 5 L). The elastomer was separated by filtration, washed with water until neutral and dried for 24 hours in vacuum at 80°C. In this way, a soft, flexible copolymer (elastomer) was obtained which contained hydrophilic polyethylene glycol regions and hydrophobic polyurethane regions.

Example 2 (a) Preparation of an intravaginal agent

An aqueous solution of fluprostenol sodium (0.1 ml at a concentration of 10 mg/ml) and an aqueous solution of C¹⁴-labelled fluprostenol sodium (5 µl at a concentration of 1 mg/ml, specific activity 133 µCi/mg) were added to a solution of the dried, pure copolymer prepared according to Example 1 (b) (2 g) in tetrahydrofuran (8 g). The mixture was homogenised by vigorous shaking. A film was cast from this mixture, dried in air at room temperature for 24 h. and finally dried in vacuum at 70°C for 8 hours. The resulting copolymer/drug film (0.02 g) containing 10 µg of drug was molded under pressure at 110°C to give a wafer (dimensions: approximately 8 mm × 7 mm × 0.2 mm). This was placed around a silicone tube (2.5 mm outer diameter × 10 mm) to give an intravaginal agent in the form of a drug-containing ring on a flexible core. When these agents were tested in rats (see below), they released the drug continuously for 24 hours. The amount of drug desorbed from the agent was measured by comparing the residual radioactivity with the original radioactivity.

(b) Determination of in vivo release

Rats (Alderley Park strain, weight 250 g) shown by vaginal smear to be in the first day of diestrus were divided into 6 groups of two animals. The animals were treated with an intravaginal agent prepared as described in Example 2(a).

The agents were removed from each group at specific time intervals and the residual radioactivity in the agents was measured. Comparison of this radioactivity with the initial radioactivity values showed that the drug was desorbed from the agent in the following manner: &udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;ta10,6:20:28,6&udf54;&udf53;tz5,5&udf54;&udf53;tw,4&udf54;&udf53;sg8&udf54;\time (st)\ % desorbed Drug&udf53;tz5,10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\Æ2\15^18&udf53;tz&udf54; \Æ4\ 22^35&udf53;tz&udf54; \Æ6\ 40^45&udf53;tz&udf54; \Æ8\ 40^46&udf53;tz&udf54; \16\ 55^62&udf53;tz&udf54; \24\ 68^72&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;

These results indicate that the drug was continuously desorbed from the devices during 24 h when the devices were introduced into the vagina of rats.

(c) Testing of intravaginal agents in rats

Rats (Alderley Park strain, weight 250 g) which had been mated with males and whose pregnancy had been confirmed by a positive sperm test on a vaginal smear were divided into four groups 6 days after mating. Animals (2) in the first group were untreated controls whose pregnancy was allowed to develop normally. Animals (6) in the second group were treated with an intravaginal agent according to the procedure of Example 2 (a) but containing no drug. Animals (6) in the third group received a single acute intravaginal dose of fluprostenol sodium (10 µg) in water (0.1 ml). Animals (8) in the fourth group were treated with an intravaginal agent prepared according to Example 2 (a) for 24 hours, after which the agents were removed. On the 15th day after mating, all animals were sacrificed and the number and health status of implantations was determined. The results are summarized in Table 1. Table 1 &udf53;np380&udf54;&udf53;vu10&udf54;&udf53;vz37&udf54;&udf53;vu10&udf54;

The two groups of control animals had healthy implants, indicating that the experimental procedure had no effect on the pregnancies. The abortion rate in rats receiving a single acute dose on day 6 was much lower (abortion rate 1/6) than in rats treated for 24 hours with the intravaginal agent (abortion rate 8/8). These results indicate that the slow release of flurprostenol sodium by the intravaginal agent of the invention produces a better effect than a single acute vaginal dose of the same drug.

Example 3 (a) Preparation of an intravaginal agent

Using the procedure described in Example 1 (a), a solution was prepared containing the elastometer described in Example 1 (b) (8 g), fluprostenol sodium (1 mg in 0.1 ml water) and C¹⁴-labeled fluprostenol sodium (20 µl of an aqueous solution with a concentration of 1 mg/ml, specific activity 133 µCi/mg) and tetrahydrofuran (34 g). After drying, a polymer/drug mixture was obtained which contained 10 µg fluprostenol sodium per 0.08 g polymer.

Individual cylinders, each Cylinders, approximately 3 mm diameter × 10 mm, were prepared by compression molding (at 110°C) 0.08 g of the polymer-drug mixture as described above. When tested in vivo in rats (see below), the cylinders released 2.2-2.5 µg of drug during 24 hr.

(b) Determination of in vivo release

Rats (Alderley Park strain, weight 250 g) shown by vaginal smear to be in diestrus were divided into 5 groups of two animals each. The animals were treated intravaginally with the agent prepared according to Example 3 (a).

The agents were removed from each group at specified intervals and the residual radioactivity in the agents was measured. Comparison of these with the initial radioactivity values showed that the drug was desorbed from the agents in the following manner: &udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;ta&udf54;&udf53;tz5,5&udf54;&udf53;tw,4&udf54;&udf53;sg8&udf54;\Time (st)\ % drug absorbed&udf53;tz5,10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\Æ2\Æ2^Æ4&udf53;tz&udf54; \Æ6\ Æ2^Æ6&udf53;tz&udf54; \12\ Æ8^10&udf53;tz&udf54; \18\ 15^18&udf53;tz&udf54; \24\ 21^26&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;

(c) Testing of the intravaginal agent in rats

Rats (Alderley Park strain, weight 250 g) which had been mated with males and whose pregnancy had been confirmed by a positive sperm test on a vaginal smear were divided into three groups on day 6 after mating. Animals (4) in the first group were controls and were treated with an empty intravaginal agent, that is, the agent had been prepared as in Example 3(a) but contained no drug. Animals (6) in the second group received a single acute intravaginal dose of fluprostenol sodium (10 µg) in a polycarboxylated gel (0.1 g). Animals (7) in the third group were each treated with an intravaginal agent prepared as in Example 3(a). 24 h later these agents were removed and comparison of the original and residual radioactivity showed that each rat had received 1.7-2.5 µg of drug within 24 h. On the 15th day after mating, all animals were sacrificed and the number and health of implantations was determined. The results are summarized in Table 2. These show that the absorption frequency using a single acute vaginal dose of 10 µg of fluprostenol sodium is 33%, but a better response of 57% is achieved when 1.7-2.5 µg of the same drug is administered over 24 hours in an intravaginal composition according to the invention. Table 2 &udf53;np290&udf54;&udf53;vu10&udf54;&udf53;vz28&udf54;&udf53;vu10&udf54;

Example 4 (a) Manufacture of intravaginal agents

Using the procedure described in Example 1 (a), the following solutions were prepared using the elastomer described in Example 1 (b):

(I) Elastomer (2 g), fluprostenol sodium (1.2 mg in 0.12 ml water), C¹⁴-labeled fluprostenol sodium (5 µl of an aqueous solution with a concentration of 1 mg/ml, specific activity 133 µCi/mg), sodium bicarbonate (1.2 mg in 60 µl water) and tetrahydrofuran (8 g).

After drying, a copolymer/drug mixture was obtained containing 12 µg fluprostenol sodium per 0.02 g copolymer.

The copolymer/drug mixture (0.02 g) was molded under pressure at 110°C to obtain a disk (dimensions: approximately 10 mm × 15 mm × 0.10 mm). This was placed around a silicone tube (4 mm outer diameter × 15 mm) to obtain an intravaginal device in the form of a ring (dimensions: approximately 10 mm long × 4 mm outer diameter and with a wall thickness of 0.1 mm) supported by a flexible core. The device contained 12 µg of drug.

(II) Using the copolymer/drug mixture (0.01 g) described in (I) above, a wafer was formed under pressure having dimensions of approximately 5 mm × 15 mm × 0.1 mm. This was placed around a silicone tube (4 mm outer diameter × 15 mm length) to obtain an intravaginal device in the form of a ring (dimensions: approximately 5 mm length × 4 mm outer diameter and with a wall thickness of 0.1 mm) supported by a flexible core. The device contained 6 µg of drug.

(III) Using the copolymer/drug mixture (0.005 g) described in (I) above, a wafer was pressure-molded having dimensions of approximately 5 mm × 8 mm × 0.1 mm. This was placed around a silicone tube (2.5 mm outer diameter × 15 mm length) to obtain an intravaginal device in the form of a ring (dimensions of approximately 5 mm length × 2.5 mm outer diameter and with a wall thickness of 0.1 mm) supported by a flexible core. The device contained 3 µg of drug.

(IV) Elastomer (4 g), fluprostenol sodium (1.2 mg in 0.12 ml water), C14-labeled fluprostenol (5 µl of an aqueous solution with a concentration of 1 µg/ml, specific activity 133 µCi/mg), sodium bicarbonate (1.2 mg in 60 µl water) and tetrahydrofuran (16 g) were mixed to prepare a solution. After drying, a copolymer/drug mixture was obtained which contained 12 µg of fluprostenol sodium per 0.04 g of copolymer. The copolymer/drug mixture (0.04 g) was molded under pressure at 110°C to obtain a platelet (dimensions: approximately 10 mm × 15 mm × 0.2 mm). This was placed around a silicone tube (4 mm outer diameter × 15 mm) to form an intravaginal device in the form of a ring (dimensions: approximately 10 mm length × 4 mm outer diameter and with a wall thickness of 0.2 mm) supported by a flexible core. The device contained 12 µg of drug.

(V) Using the copolymer/drug mixture (0.02 g) described in (IV) above, a wafer was molded under pressure having dimensions of approximately 5 mm × 15 mm × 0.2 mm. This was placed around a silicone tube (4 mm outer diameter × 15 mm) to obtain an intravaginal device in the form of a ring (dimensions: approximately 5 mm length × 4 mm outer diameter and with a wall thickness of 0.2 mm) supported by a flexible core. The device contained 6 µg of drug.

(VI) Using the copolymer/drug mixture (0.01 g) described in (IV) above, a wafer was molded under pressure having dimensions of approximately 5 mm × 8 mm × 0.2 mm. This was placed around a silicone tube (2.5 mm outer diameter × 15 mm length) to obtain an intravaginal device in the form of a ring (dimensions of approximately 5 mm length × 2.5 mm outer diameter and with a wall thickness of 0.2 mm) supported by a flexible core. The device contained 3 µg of drug.

(VII) Using the copolymer/drug mixture (0.004 g) described in (IV) above, a wafer was molded under pressure having dimensions of approximately 2 mm × 8 mm × 0.2 mm. This was placed around a silicone tube (2.5 mm outer diameter × 15 mm) to obtain an intravaginal device in the form of a ring (dimensions of approximately 2 mm × 2.5 mm outer diameter and with a wall thickness of 0.2 mm) supported by a flexible core. The device contained 1.2 µg of drug.

(b) Determination of in vivo release

In a series of experiments, rats (Alderley Park strain, weighing 200 g), shown by a vaginal smear to be in the 1st day of diestrus, were divided into groups of two animals. The animals were treated with the agents described in Example 4 (a). The agents were removed from each group at specified intervals and the residual radioactivity in the agents was determined. Comparison of the residual radioactivity with the initial radioactivity values showed that the drug was desorbed from the agents in the following manner: For agents (I), (II) and (III) &udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;ta&udf54;&udf53;tz5,5&udf54;&udf53;tw,4&udf54;&udf53;sg8&udf54;\Time (st)\ % drug desorbed&udf53;tz5,10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\2\25^40&udf53;tz&udf54; \5\ 40^60&udf53;tz&udf54; \8\ 72^92&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;The agents were removed after 8 hr. For agents (IV), (V), (VI) and (VII) &udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;ta&udf54;&udf53;tz5,5&udf54;&udf53;tw,4&udf54;&udf53;sg8&udf54;\Time (st)\ %Drug desorbed&udf53;tz5,10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\Æ4\21^36&udf53;tz&udf54; \Æ8\ 36^55&udf53;tz&udf54; \16\ 65^83&udf53;tz&udf54; \24\ 67^92&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;The funds were removed after 24 hours.

These results indicate that for agents (I), (II) and (III), the drug was continuously desorbed from the agents for 8 hours when they were inserted into the vagina of rats. For agents (IV), (V), (VI) and (VII), the drug was continuously desorbed from the agents for 24 hours when they were inserted into the vagina of rats.

(c) Testing of intravaginal agents in rats

Rats (Alderley Park strain, weight 250 g) that had been placed with males and whose pregnancy had been confirmed by a positive sperm test on a vaginal smear were divided into groups and treated on the 6th day after mating in the following manner:

Group 1. Untreated; the pregnancy was allowed to develop normally.

Group 2. Treated with 0.1 ml polycarboxylate gel containing no drug.

Group 3. Treated with intravaginal agents prepared according to Example 4 (a) but containing no drug.

Group 4. Treated with 0.1 ml of polycarboxylate gel containing no drug.

Group 5. Treated with agent (I), (II) or (III). The drug was administered for 8 hours, after which the agents were removed.

Group 6. Treated with agent (IV), (V), (VI) or (VII). The drug was administered for 24 hours, after which the agents were removed.

In animals in groups 5 and 6, the amount of drug delivered was measured by comparing residual radioactivity with initial levels. On day 15 after mating, all animals were sacrificed and the number and health of implantations was determined. The results are summarized in Table 3. Table 3 Rats treated on day 6 of pregnancy. Acute dose versus sustained release. &udf53;np290&udf54;&udf53;vu10&udf54;&udf53;vz28&udf54;&udf53;vu10&udf54;

The results show that the incidence of abortion in pregnant rats was higher when treated with the sustained-release agents and that, at comparable doses, response increased as the duration of administration was extended.

Example 5 (a) Production of copolymers

Polyethylene glycol with a molecular weight of 4000 was purified according to the procedure of Example 1. The purified dry product had a hydroxyl value of 27.6 mg KOHg ^-1 . 1,1'-Isopropylidene-bis-p-phenyleneoxydipropan-2-ol was purified using a similar procedure as that used for polyethylene glycol. 4,4'-Diphenylmethane diisocyanate was distilled (bp 160-170°C/0.1 mg Hg) before use.

Using the purified materials, the following elastomers were produced:

A. Polyethylene glycol (51 g) and the above-mentioned bisphenol derivative (28 g) were mixed at 80°C and the diisocyanate (23 g) was added. The mixture was then thoroughly mixed by stirring and then reacted at 80°C for 36 hours under dry nitrogen. The mixed polymer was cooled to room temperature and allowed to post-cure for 3 days to obtain an elastomeric product. The elastomer contained 50 wt.% hydrophilic blocks and 50 wt.% hydrophobic blocks.

B. Polyethylene glycol (40 g) and the above-mentioned bisphenol derivative (14.1 g) were reacted with the diisocyanate (12.5 g) at 80°C in the manner described above. The resulting elastomer contained 60 wt.% hydrophilic blocks and 40 wt.% hydrophobic blocks.

C. Polyethylene glycol (60 g) and the above-mentioned bisphenol derivative (15 g) were reacted with the diisocyanate (15 g) at 80°C in the manner described above. The resulting elastomer contained 67 wt.% hydrophilic blocks and 33 wt.% hydrophobic blocks.

(b) Cleaning of elastomers

Elastomers A, B and C were purified as follows:

The elastomer (50 g) was dissolved in a mixture of absolute ethanol (400 g) and distilled water (100 g) at 70°C. Sodium carbonate (0.1 g in 2 ml water) was added and the mixture was stirred for 2 h at 70°C. The solution was added to distilled water (5 L) to precipitate the interpolymer. The mixture was filtered and the solid residue was washed with distilled water (2 L). The solid was then stirred in distilled water (3 L) for 24 h, filtered and dried in vacuum at 80°C.

(c) Preparation of copolymer/drug mixtures

The following procedure was carried out with each of the copolymers A, B and C:

Solutions of fluprostenol sodium (3 mg) in water (0.3 ml), C14-labeled fluprostenol sodium (80 µl at a concentration of 0.02 mg/ml, specific activity 133 µCi/mg) in water and sodium bicarbonate (60 µl of a solution of 50 mg/ml) in water were added to a solution of the copolymer (3 g) in tetrahydrofuran (30 ml). The mixture was cast on a film and dried in air at room temperature for 24 h and then in vacuum at 70°C for 8 h. The resulting copolymer/drug mixture was molded under pressure at 110°C to give platelets 0.16 cm thick.

(d) In vitro delivery of the drug

The desorption of the drug and the radioactivity of 0.5 g of the mentioned platelets were determined in the following manner:

The copolymer/drug disks (0.5 g) were concentrated by a stirrer in 500 ml of phosphate solution buffered to pH 7 (prepared from 3.7 g potassium hydrogen phosphate and 5.78 g disodium hydrogen orthophosphate dihydrate in 1000 ml water) and maintained at 37°C. Using a stirring speed of 100 rpm, the desorption of radioactivity was shown to be approximately ^1/2 proportional to time. The equilibrium swelling of the copolymer at 37°C in water was:
Mixed polymer A approx. 100%
Mixed polymer B approx. 150%
Copolymer C approx. 210%

Example 6 (a) Manufacture of intravaginal agents

The following copolymer/drug mixtures were prepared using the elastomer described in Example 5 (Copolymer A):

(I) Elastomer (3 g), fluprostenol sodium (1.2 mg in 0.12 ml water), C¹⁴-labeled fluprostenol sodium (15 µl of an aqueous solution with a concentration of 1 mg/ml, specific activity 133 µCi/mg), sodium bicarbonate (1.2 mg in 60 µl water) and tetrahydrofuran (13 g). After drying, a copolymer/drug mixture was obtained which contained 12 µg fluprostenol sodium per 0.03 g copolymer.

The copolymer/drug mixture (0.03 g) was molded under pressure at 110°C to obtain a wafer (dimensions: approximately 7 mm × 15 mm × 0.2 mm). This was placed around a silicone tube (4 mm outer diameter × 15 mm) to obtain an intravaginal device in the form of a ring (dimensions: approximately 7 mm × 4 mm outer diameter and with a wall thickness of 0.2 mm) supported by a flexible core. The device contained 12 µg of drug.

(II) Using the copolymer/drug mixture (0.015 g) described in (I) above, a wafer was molded under pressure having dimensions of approximately 4 mm × 15 mm × 0.2 mm. This was placed around a silicone tube (4 mm outer diameter × 15 mm) to obtain an intravaginal device in the form of a ring (dimensions of approximately 4 mm × 4 mm outer diameter and with a wall thickness of 0.2 mm) supported by a flexible core. The device contained 6 µg of drug.

(III) Elastomer (1.5 g), fluprostenol sodium (1.2 mg in 0.12 ml water), C¹⁴-labeled fluprostenol sodium (2 µl of an aqueous solution with a concentration of 1 mg/ml, specific activity 133 µCi/mg), sodium bicarbonate (1.2 mg in 60 µl water) and tetrahydrofuran (5 g) were mixed to prepare a solution. After drying, a copolymer/drug mixture was obtained which contained 6 µg fluprostenol sodium per 0.0075 g copolymer. The copolymer/drug mixture (0.0075 g) was molded under pressure at 110°C into a plate (dimensions: approximately 7 mm × 8 mm × 0.1 mm). This was placed around a silicone tube (2.5 mm outer diameter × 15 mm length) to obtain an intravaginal agent in the form of a ring (dimensions: approximately 7 mm × 2.5 mm outer diameter and with a wall thickness of 0.1 mm) supported by a flexible core. In non-pregnant rats, intravaginal agents (I) and (II) released 70-90% of the drug in 24 h, while intravaginal agent (III) released 70-90% in 8 h.

(b) Testing of intravaginal agents in rats

Rats (Alderley Park strain, weight 250 g) which had been placed with males and whose pregnancy had been confirmed by positive sperm test of a vaginal smear were divided into groups and on the 9th day after mating they were treated in the following manner:

Group 1. Untreated; the pregnancy was allowed to develop normally.

Group 2. Treated with 10 µg fluprostenol sodium in 0.05 ml polycarboxylate gel.

Group 3. Treated with a drug containing 12 µg of drug and delivered in 24 hrs.

Group 4. Treatment with 5 µg fluprostenol sodium in 0.1 mg polycarboxylate gel.

Group 5. Treatment with a drug containing 6 µg of drug administered continuously for 24 hours.

Group 6. Treated with an agent containing 6 µg of drug, with 70-90% of the drug released in 8 hr.

The agents in groups 5 and 6 were removed after 24 hrs and the residual radioactivity was measured. Comparison of these with the initial values allowed the calculation of the amount of drug released. On the 20th day after fertilization, all animals were sacrificed, after which the number and health status of implantations were determined. Table 4 Rats treated on the 9th day of pregnancy. Acute dosing versus sustained release &udf53;np160&udf54;&udf53;vu10&udf54;&udf53;vz15&udf54;&udf53;vu10&udf54;

These results indicate that a prolonged duration of drug administration results in a higher abortion rate.

Example 7 (a) Preparation of an intravaginal agent

The following copolymer/drug mixtures were prepared using the elastomer described in Example 5 (Copolymer A):

Elastomer (5 g), fluprostenol sodium (12 mg in 1.2 ml water), C¹⁴-labeled fluprostenol (1 µl of an aqueous solution with a concentration of 1 mg/ml, specific activity 133 µCi/mg), sodium bicarbonate (12 mg in 600 ml water) and tetrahydrofuran (50 g). After drying, a copolymer/drug mixture was obtained which contained 300 µg fluprostenol sodium per 0.125 g copolymer. The copolymer/drug mixture (0.125 g) was formed under pressure into a plate (dimensions: approximately 15 mm × 7 mm × 1 mm). This was placed around a silicone tube (4 mm outer diameter × 60 mm length) to form an intravaginal device in the form of a ring (dimensions: approximately 7 mm × 6 mm outer diameter and with a wall thickness of 1 mm) supported by a flexible core. The device contained 300 µg of drug.

(b) Determination of in vivo release

Female Stöbers (small dogs) (weighing approximately 12-15 kg) were treated with intravaginal agents described in Example 6 (a). Agents were removed from individual dogs at specified time intervals and residual radioactivity was measured. Comparison of these with initial radioactivity values showed that drug was desorbed from the agents in the following manner: &udf53;sb37.6&udf54;&udf53;el1.6&udf54;&udf53;ta&udf54;&udf53;sg8&udf54;&udf53;tz5.5&udf54;&udf53;tw.4&udf54;\time (st)\ % drug desorbed&udf53;tz5.10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\Æ5\30&udf53;tz&udf54; \16\ 63&udf53;tz&udf54; \24\ 80&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;

These results indicate that the drug was continuously desorbed from the devices during 24 hours when the devices were introduced into the vagina of dogs.

(c) Testing an intravaginal agent in pregnant dogs

Female snouts (weight 12-19 kg) that had been paired with males and whose pregnancy had been confirmed by palpation were divided into 3 groups 25 days after mating.

Group 1. These animals were treated on the 25th and 26th day of pregnancy with ring-shaped devices that had a wall thickness of 1 mm and released approximately 20-25 µg/kg fluprostenol sodium during 24 h.

Group 2. These animals were treated on day 25 with ring-shaped devices that had a wall thickness of 1 mm and released approximately 20-25 µg/kg fluprostenol sodium during 24 h.

Group 3. These animals were treated on the 25th and 26th day of pregnancy with ring-shaped devices that had a wall thickness of 1 mm and released approximately 10 µg/kg fluprostenol sodium during 24 h.

Blood samples were taken from all animals in the three groups before, during and after treatment for progesterone determination. Animals were palpated 1 week and 2 weeks after treatment to determine regression of implantations. The results are summarized in Table 5. Table 5 Treatment of pregnant dogs with sustained-release intravaginal agents &udf53;np200&udf54;&udf53;vu10&udf54;&udf53;vz19&udf54;&udf53;vu10&udf54;

A comparison of the frequency of abortions in groups 1 to 3 shows that the duration of administration is an important feature of treatment and that administration of the drug for 48 hours results in a better abortion rate than when the treatment lasts 24 hours.

Example 8

The dogs of Example 7 which did not experience abortion were treated with sustained release intravaginal agents containing fluprostenol sodium. The animals were treated on day 57 of pregnancy with the ring-shaped agents described in Example 7. These agents were formulated to deliver 20 to 25 µg/kg of drug for 24 hours when inserted into the vagina of pregnant dogs. The agents were removed 24 hours later. The results are summarized in Table 6. Table 6 Induction of Labor in Pregnant Dogs &udf53;np120&udf54;&udf53;vu10&udf54;&udf53;vz11&udf54;&udf53;vu10&udf54;

In all cases, labor was induced and all animals gave birth to lively, healthy puppies.

Example 9 (a) Preparation of a copolymer/drug mixture

Copolymer (B, as described in Example 5, 3.6 g), fluprostenol sodium (10 mg, i.e. 2 ml of a 5 mg/ml solution) in water, C¹⁴-labeled fluprostenol sodium (5 µl of a 0.02 mg/ml solution in water, specific activity 133 µCi/mg) and 200 µl of buffer solution (pH 7: a solution of 3.9 g of potassium hydrogen orthophosphate and 6.1 g of disodium hydrogen orthophosphate dihydrate in 100 ml of distilled water) were dissolved in a mixture of absolute ethanol (18 ml) and distilled water (3.6 ml) at 70°C. The solution was cast into a film which was dried at room temperature for 18 h in air and then in vacuum at 80°C for 8 h.

(b) Determination of in vivo delivery

The interpolymer/drug mixture was molded under pressure at 110°C into wafers (0.16 cm thick) and disks (weighing approximately 0.145 g) were cut from the wafer. The use of these disks as sustained release intravaginal agents was tested in non-pregnant dogs.

Animals were divided into 4 groups of two and the agents were placed deep in the vaginal vault of the animals. After 1, 2, 5 and 8 hrs the agents were removed and the residual radioactivity was measured. Comparison of these with the original values showed that the agents released the drug continuously for 8 hrs. The results are summarized as follows: &udf53;sb37.5&udf54;&udf53;el1.6&udf54;&udf53;ta&udf54;&udf53;tz5.5&udf54;&udf53;tw.4&udf54;&udf53;sg8&udf54;\time (hrs)\ % drug desorbed from the agent&udf50;tz5.10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\1\23^28&udf53;tz&udf54; \2\ 44^49&udf53;tz&udf54; \5\ 58^64&udf53;tz&udf54; \8\ 65^80&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;sg9&udf54;&udf53;vu10&udf54;

The incorporation of a buffer into the agent maintained the pH of the vagina at 6-7 during the delivery period and ensured reproducibility of the drug delivery.

Example 10

These hydrophilic copolymers also act as drug delivery vehicles for drugs with very low water solubility. This can be demonstrated using progesterone.

(a) Preparation of a copolymer/drug mixture

Progesterone (10 mg), progesterone labeled to 10 µCi with C¹⁴-labeled (60.7 µCi/mmol in 530 µl benzene) and the blend polymer (Example 5, blend polymer B; 1 g) were dissolved in tetrahydrofuran (10 ml). The solution was dried in air at room temperature for 18 h and finally in vacuum at 80°C for 8 h. The resulting blend polymer/drug mixture was molded at 110°C to give a film 0.02 cm thick.

(b) In vitro delivery of the drug

0.2 g of the film was suspended on the end of a stirrer in 500 ml of distilled water at 37°C. The stirring speed was 150 rpm. The desorption of the drug over time was determined by measuring the radioactivity in the distilled water. After 24 hrs, the swollen film was dissolved in tetrahydrofuran and the residual radioactivity was measured. The desorption of the drug over time is summarized as follows: &udf53;sb37.6&udf54;&udf53;el1.6&udf54;&udf53;ta&udf54;&udf53;tz5.5&udf54;&udf53;tw.4&udf54;&udf53;sg8&udf54;\time (hrs)\ % progesterone desorbed&udf53;tz5.10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\Æ1\Æ8&udf53;tz&udf54; \Æ2\ 13&udf53;tz&udf54; \Æ3\ 18&udf53;tz&udf54; \Æ9\ 24&udf53;tz&udf54; \17\ 33&udf53;tz&udf54; \24\ 34&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;

Desorption of progesterone from the agent was determined by the polymer carrier and also by the low solubility of progesterone in distilled water. When the distilled water was continuously changed to maintain "sinking conditions", then almost complete release of progesterone was achieved.

Example 11

This example illustrates the further use of a hydrophilic interpolymer as a drug delivery vehicle for a drug of low water solubility [tamoxifen citrate, i.e., 1-(p -β- dimethylaminoethoxyphenyl)-1,2-trans-diphenylbut-1-ene citrate].

(a) Preparation of a copolymer/drug mixture

C¹⁴-labeled tamoxifen citrate (10 mg; specific activity 0.33 µCi/mg) and copolymer (Example 5, copolymer B; 1 g) were dissolved in tetrahydrofuran (10 ml). The solution was dried at room temperature for 18 h in air and finally for 8 h in vacuum at 80°C. The copolymer/drug mixture was molded at 110°C into a film with a thickness of 0.02 cm.

(b) In vitro delivery of the drug

Using the procedure described in Example 10(b), but using the tamoxifen citrate/copolymer mixture, the following results for drug desorption were obtained: &udf53;sb37.6&udf54;&udf53;el1.6&udf54;&udf53;ta10.6:24:28.6&udf54;&udf53;tz5.5&udf54;&udf53;tw.4&udf54;&udf53;sg8&udf54;\Time (hrs)\ % desorbed&udf53;tz5.10&udf54;&udf53;tw.4&udf54;&udf53;sg9&udf54;\Æ0.1\Æ6&udf53;tz&udf54; \Æ0.2\ 16&udf53;tz&udf54; \Æ0.5\ 23&udf53;tz&udf54; \Æ1\ 34&udf53;tz&udf54; \Æ3\ 39&udf53;tz&udf54; \17\ 42&udf53;tz&udf54; \72\ 50&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;

This indicates that tamoxifen citrate, which is slightly soluble in water, can be released from the above copolymer in a delayed manner.

Claims (11)

1. Agent for the delayed release of a biologically active substance into a human or animal body, which agent contains I a biologically active substance, II a polymeric carrier material and III, if appropriate, a biologically acceptable buffer, characterized in that the polymeric carrier material II is a linear hydrophilic polyoxyalkylene/polyurethane block copolymer which is largely free of crosslinking and is composed of several hydrophilic and hydrophobic regions, in which the hydrophilic regions consist of one or more polyoxyalkylenes with the repeat units -(CH₂)₂O-, -CH₂CH(CH₃)O-, -(CH₂)₃O- and/or -(CH₂)₄O- and the hydrophobic regions consist of a polyurethane obtainable in a known manner by reacting a diisocyanate with one or more dihydroxy compounds, the active substance I and, if appropriate, the buffer III being distributed in the carrier. 2. Agent according to claim 1, characterized in that the polyoxyalkylene is a polyoxyethylene having a molecular weight of 400 to 20,000. 3. Agent according to one of claims 1 or 2, characterized in that the hydrophobic regions consist of a polyurethane which is obtainable in a known manner from an aromatic or aliphatic diisocyanate and one or more dihydroxy compounds. 4. Agent according to claim 3, characterized in that the diisocyanate consists of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate or 4,4'-dicyclohexylmethane diisocyanate. 5. Agent according to one of claims 3 or 4, characterized in that the dihydroxy compound or dihydroxy compounds is/are selected from alkylene glycols having not more than 6 carbon atoms and short-chain oxyalkylated diphenols. 6. Agent according to claim 5, characterized in that the alkylene glycol consists of ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol or 1,4-butylene glycol. 7. Agent according to claim 5, characterized in that the oxyalkylated diphenol consists of 1,1'-isopropylidene-bis-p-phenyleneoxydipropan-2-ol. 8. Agent according to one of claims 1 to 7, characterized in that the copolymer contains 30 to 70 wt.% hydrophilic regions and 70 to 30 wt.% hydrophobic regions. 9. Agent according to claim 2, characterized in that the polyoxyethylene has a molecular weight of 600 to 6000. 10. Agent according to one of claims 1 to 9, characterized in that the mixed polymer contains 30 to 70% by weight of hydrophilic regions and 70 to 30% by weight of hydrophobic regions, the hydrophilic regions consist of polyoxyethylene with a molecular weight of 600 to 6000 and the hydrophobic regions consist of a polyurethane which can be obtained in a known manner by reacting 4,4'-diphenylmethane diisocyanate with 1,1'-isopropylidene-bis-p-phenyleneoxydipropan-2-ol. 11. Agent according to claim 1, characterized in that the biologically active substance consists of the prostaglandin derivative fluprostenol sodium, that it contains a biologically acceptable buffer and that the copolymer contains 60% by weight of polyoxyethylene with a molecular weight of 4000 and 40% by weight of hydrophobic polyurethane blocks, the latter having been obtained in a known manner from approximately equal parts by weight of 4,4'-diphenylmethane diisocyanate and 1,1'-isopropylidene-bis-p-phenyleneoxy-dipropan-2-ol.